My 22 wildcat goes thru a breach seal o-ring every 2500 shots like clock work. Just went thru my 3rd one. I'm tired of looking for the size, so I'll just ask. I think it is 5.28x1.78 but not sure. There is a big hydraulic and air cylinder place not far away so was going to check with them and see if they had it in different materials to try. Maybe this is where I should go into a rant about FX. Just kidding. Couldn't be happier with them and this gun this gun.